Multitrack disk player and method of read error recovery

ABSTRACT

An error recovery method and an apparatus achieve error recovery when reading errors occur at one or more addresses on a plurality of simultaneously readable tracks, in a multi-track disk reproducing apparatus. The reproducing apparatus with a plurality of reading head can simultaneously read data on the plurality of adjacent tracks on a disk having the plurality of tracks formed on its recording surface. The method comprises a step for storing a reading error-occurrence-address in an error occurrence, and a step for determining a moving process of the plurality of reading head for error recovery after the error occurrence based on the stored result.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP99/06980.

FIELD OF THE INVENTION

The present invention relates to a multi-track disk reproducingapparatus that transfers data at a high speed by simultaneously readinga plurality of tracks.

BACKGROUND OF THE INVENTION

Conventionally, as a means for increasing a data transfer rate of anoptical disk system, a method (it is hereinafter called a multi-beammethod) for simultaneously reproducing a plurality of tracks on anoptical disk is suggested.

More specifically, this method is used to increase the data transferrate in the following processes:

(1) A plurality of adjacent tracks are simultaneously read using anoptical pickup constituted with plural pairs of light emitting elementsand light receiving elements;

(2) The read data are stored in a buffer memory;

(3) The stored data are read out in the same order as the alignment ofthe tracks on the optical disk.

A conventional multi-beam method is hereinafter described in moredetails.

FIG. 1 is a block diagram of an optical disk reproducing apparatus forreproducing an optical disk in the conventional multi-beam method. Thisexample shows an apparatus capable of simultaneously reading data onfour tracks. The reproducing apparatus comprises the following elements:

(a) optical disk 1 on which tracks are formed concentrically orspirally,

(b) spindle motor 2 for supporting and rotating optical disk 1,

(c) light emitting elements 31, 32, 33, 34 for respectively radiatinglaser beams to four adjacent tracks on rotating optical disk 1,

(d) light receiving elements 41, 42, 43, 44 that receive reflectedlights from respective irradiated tracks and convert them to electricsignals,

(e) optical pickup 5 constituted with light emitting elements 31, 32,33, 34 and light receiving elements 41, 42, 43, 44,

(f) feed motor 6 for moving optical pickup 5 radially of optical disk 1,

(g) reproducing circuits 71, 72, 73, 74 for respectively reproducingindependent data read simultaneously from four tracks, based on electricsignals supplied from optical pickup 5,

(h) memory control circuit 8 that temporarily stores the independentdata reproduced by reproducing circuits 71, 72, 73, 74 in buffer memory9, reads out the reproduced data stored in buffer memory 9 in the sameorder as the alignment of the tracks on optical disk 1, and transmits itto host interface 10,

(i) host interface 10 for receiving reproducing instructions ortransmitting the reproduced data from/to a host device through terminal11, and

(j) controller 12 for controlling the elements discussed above.

These elements are configured as shown in FIG. 1.

In this example, simultaneous reading of four tracks is usually allowed,but a reading error occurs in some compact disk—read only memory(CD-ROM) device. Recently, even an individual user has been able towrite data onto a CD-ROM disk thanks to diffusion of a CD-R or the like,but disks are widespread which have extremely bad recording statesdepending on poor characteristic compatibility between a CD-R media anda CD-R drive, or recording speeds. On such CD-ROM device, erroroccurrence is hardly prevented even by a strongerror-correcting-function of the CD-ROM. In addition, a reading errormay occur because of a large flaw on the disk or a defect during itsmanufacture.

When such reading error occurs in a conventional CD-ROM device whosesingle track is read, generally, its head is immediately returned to thetrack having the error to try rereading, and the reproducing rate issimultaneously decreased to try reproduction. At this time, however,there is a problem that the reproduction is interrupted to extremelydecrease the reading rate. In addition, the similar method is used evenfor a CD-ROM device whose plural tracks are reproduced simultaneously,and therefore, the similar problem occurs.

DISCLOSURE OF THE INVENTION

For resolving the conventional problem discussed above, a reading-errorrecovery method in accordance with the present invention has thefollowing characteristics. First, among a plurality of reading meanscapable of simultaneously reading, the tailing reading means is used forrereading an error-occurrence-address, and the heading reading meanscontinues to read data in an unread region. Next, when the rereading ofthe error-occurrence-address is completed, depending on number of unreadtracks assigned to the plurality of reading means during the rereadingof the error-occurrence-address and on an error occurrence position onthe track, selective switching is performed between the followingprocesses:

Track jump is carried out immediately and larger number of reading meansare assigned to the unread tracks even during the rereading of theerror-occurrence-address;

The tracks being read are continuously reproduced without performing anytrack-jump.

The present invention can restrain reduction of the reading rate to aminimum even when an error occurs and the rereading of theerror-occurrence-address is tried.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional multi-track disk reproducing apparatus.

FIG. 2 shows a multi-track disk reproducing apparatus in accordance withthe present invention.

FIG. 3 is a track alignment diagram of an information disk on whichtracks are concentrically formed.

FIG. 4 is a track alignment diagram of an information disk on whichtracks are spirally formed.

FIG. 5 is a schematic flowchart during a reproducing operation of theapparatus in accordance with the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION Preferred embodiment 1

The embodiment 1 of the present invention is described hereinafter withreference to FIG. 2, FIG. 3, FIG. 4, and FIG. 5.

FIG. 2 is a block diagram of an optical-disk-reproducing-apparatus forreproducing an optical disk in a multi-beam method in accordance withthe present invention.

FIG. 3 is a track alignment diagram of an information disk on whichtracks are concentrically formed, and reproducing beams 51, 52, 53, 54respectively trace tracks Tn, Tn+1, Tn+2, Tn+3.

Reproducing beams 51, 52, 53, 54 move left with respect to the disk withrotation of the disk, and return to their original positions after onerotation.

FIG. 4 is a track alignment diagram of an information disk on whichtracks are spirally formed, and reproducing beams 51, 52, 53, 54respectively trace tracks Tn, Tn+1, Tn+2, Tn+3. Reproducing beams 51,52, 53, 54 move left with respect to the disk with rotation of the disk,and respectively reach the tops of tracks Tn+1, Tn+2, Tn+3, Tn+4 afterone rotation.

In FIG. 2, the reproducing apparatus comprises the following elements:

(a) optical disk 1 on which tracks are formed concentrically orspirally,

(b) spindle motor 2 for supporting and rotating optical disk 1,

(c) light emitting elements 31, 32, 33, 34 for respectively radiatinglaser beams to four adjacent tracks on rotating optical disk 1,

(d) light receiving elements 41, 42, 43, 44 that receive reflectedlights from respective irradiated tracks and convert them to electricsignals,

(e) optical pickup 5 constituted with light emitting elements 31, 32,33, 34 and light receiving elements 41, 42, 43, 44,

(f) feed motor 6 for moving optical pickup 5 radially of optical disk 1,

(g) reproducing circuits 71, 72, 73, 74 for respectively reproducingindependent data read simultaneously from four tracks, based on electricsignals supplied from optical pickup 5,

(h) memory control circuit 8 that temporarily stores the independentdata reproduced by reproducing circuits 71, 72, 73, 74 in buffer memory9, reads out the reproduced data stored in buffer memory 9 in the sameorder as the alignment of the tracks on optical disk 1, and transmits itto host interface 10,

(i) reading-error-occurrence-address-memory 20 for storingerror-occurrence-addresses when the reading error occurs,

(j) host interface 10 for receiving reproducing instructions ortransmitting the reproduced data from/to a host device through terminal11, and

(k) controller 12 for controlling the elements discussed above.

These elements are configured as shown in FIG. 2.

A basic reproducing operation is described hereinafter. When hostinterface 10 receives the reproducing instructions for adjacent tracksT1 to T4 on optical disk 1 from the host device through terminal 11,controller 12 performs the reproducing operation by sending theinstructions to each element. To be more specific, controller 12controls feed motor 6 to move optical pickup 5 so as to respectivelyradiate laser beams from light emitting elements 31, 32, 33, 34 totracks T1, T2, T3, T4 on optical disk 1 rotated by spindle motor 2. Atthis time, respective reflected lights are converted to electric signalsby light receiving elements 41, 42, 43, 44, and these electric signalsare further sent to reproducing circuits 71, 72, 73, 74 to beindependently reproduced. In the following description, a disk on whichdata is recorded from the inner radius to the outer radius isillustrated. In a recording order of the data, a reading means and atrack which are positioned at the inner radius side on the disk arerespectively called a tailing reading means and a tailing track, and areading means and a track which are positioned at the outer radius sideon the disk are respectively called a heading reading means and aheading track. If data is recorded from the outer radius to the innerradius, the relations between these designations and the positions onthe disk are reverse. The reproduced independent data for respectivetracks is temporarily stored in buffer memory 9 via memory controlcircuit 8, then is read out in the same order as the alignment of thetracks on optical disk 1, i.e. in the order of T1, T2, T3, T4, and issent to the host device through host interface 10 and terminal 11. Whena reading error occurs here, an address of the error position is storedin reading-error-occurrence-address-memory 20.

Rereading operations of the error-occurrence-address are describedhereinafter.

(1) Error recovery of a disk on which data is concentrically recorded asshown in FIG. 3.

The data is recorded on tracks T1, T2, T3 . . . sequentially from theinner track. A case that the data on T2 and later is read out every fourtracks is considered.

Because four tracks can be simultaneously reproduced, the data on T2,T3, T4, T5 is simultaneously read out. Reproducing beams 51, 52, 53, 54,light receiving elements 41, 42, 43, 44, and reproducing circuits 71,72, 73, 74 respectively correspond to T2, T3, T4, T5.

Here, it is assumed that an error occurs on T5. When the error isdetected at a part of T5, the error-occurrence-address is stored inmemory 20, reproduction of T2, T3, T4, T5 is continued without anytrack-jump until data corresponding to one circumference of each trackhas been read, and reproduced data is written into the buffer memory. Atthis time, the data on T2, T3, T4 and the data before theerror-occurrence-address on T5 have already been read without any error,are continuous data from the top data, and therefore, are allowed to betransferred to the host interface.

For rereading the error-occurrence-address on T5, it must be determinedwhether a track-jump is performed or not. Because the disk rotates evenduring the track-jump when the error-occurrence-address is at the top ofT5, last tailing reproducing beam 51 may travel past theerror-occurrence-address.

In this case, two options can be selected: an option that rereading istried by the original light receiving element and reproducing circuitwithout any track-jump; and an option that the track-jump is performed,then the track after the jump is read, and finally rereading is tried.

In the option of performing the track-jump, the track-jump is carriedout so as to read T5, T6, T7, T8. At this time, reproducing beams 51,52, 53, 54 respectively correspond to T5, T6, T7, T8. Reproducing beam51 waits until the error-occurrence-address on T5 reaches the beamposition with rotation, and tries to reread theerror-occurrence-address. When the rereading can be performed, the datais written into a corresponding address in the buffer memory, and isallowed to be transferred to a host. At this time, heading reproducingbeams 51, 52, 53, 54 can continue to reproduce unread tracks T6, T7, T8,and the reproducing rate becomes ¾ of the normal rate.

Even when number of simultaneously readable tracks is larger or smaller,heading light receiving elements (positioned on the outer radius side ofthe track assigned for reading of the error-occurrence-track) andreproducing circuits (corresponding to these light receiving elements)can similarly continue to reproduce the unread region. When readingerrors occur at a plurality of addresses, heading light receivingelements and reproducing circuits can similarly continue to reproducethe unread region by performing the following process: a track-jump isperformed on the basis of the earliest heading error-occurrence-addresson the last tailing track (positioned on the innermost radius side) oferror-occurrence-tracks, i.e. an error-occurrence-address at which thelight receiving elements earliest arrive from the tops of the trackswith rotation of the disk.

(2) Error recovery of a disk on which data is spirally recorded as shownin FIG. 4.

A case that the data on T2 and later is read out every four tracks isconsidered.

Because four tracks can be simultaneously reproduced, the data on T2,T3, T4, T5 is simultaneously read out. Reproducing beams 51, 52, 53, 54,light receiving elements 41, 42, 43, 44, and reproducing circuits 71,72, 73, 74 respectively correspond to T2, T3, T4, T5.

First, the operation in a case that an error occurs on T5 is described.When the error is detected on T5, the error-occurrence-address is storedin memory 20, the reproduction of T2, T3, T4, T5 is continued until datacorresponding to one circumference of each track has been read, and thereproduced data is written into the buffer memory. At this time, thedata on T2, T3, T4 and before the error-occurrence-address on T5 hasalready been read without any error, is continuous data from the topdata, and therefore, is allowed to be transferred to the host interface.

Then, a track-jump is performed so as to reread theerror-occurrence-address on T5. However, because the data is spirallyrecorded, respective light receiving elements and reproducing circuitshave reached the tops of T3, T4, T5, T6 when data for one rotation isfinished to be read. If an error has occurred at the top of T5, theerror-occurrence-address has already been passed when the track-jump isfinished because the disk further continues to rotate even during thetrack-jump. Therefore, quantity of the track-jump and the selectionwhether the track-jump is performed or not must be selected responsiveto the error-occurrence-address.

When an error occurs near the top of T5 and the error-occurrence-addresscan be passed after the track-jump, the track-jump is performed so as toread T4, T5, T6, T7. At this time, reproducing beams 51, 52, 53, 54respectively correspond to T4, T5, T6, T7. Because the tail end of T4 ispositioned at the top of T5, the last tailing reproducing beam 51 waitsuntil the error-occurrence-address reaches the beam position withrotation, and tries to reread the error-occurrence-address. When therereading can be performed, the data is written into a correspondingaddress in the buffer memory, and is allowed to be transferred to ahost. Because the tail end of T5 is positioned at the top of T6,reproducing beam 52 waits until to the top of T6 reaches it, andcontinues to read data at the top of T6 passed during the track-jump.Heading reproducing beams 53, 54 can continue to reproduce unread tracksT6, T7, and the reproducing rate becomes ½ of the normal rate.

When an error occurs satisfactorily far away from the top of T5 and theerror-occurrence-address is hardly passed after the track-jump, thetrack-jump is performed so as to read T5, T6, T7, T8. At this time,reproducing beams 51, 52, 53, 54, light receiving elements 41, 42, 43,44, and reproducing circuits 71, 72, 73, 74 respectively correspond toT5, T6, T7, T8. Latest tailing reproducing beam 51 waits until theerror-occurrence-address on T5 reaches the beam position with rotation,and tries to reread the error-occurrence-address. When the rereading canbe performed, the data is written into a corresponding address in thebuffer memory, and is allowed to be transferred to a host.

In addition, because the tail end of T5 is positioned at the top of T6,reproducing beam 51 reproduces data close to the top of T6 past whichreproducing beam 52 travels. Heading reproducing beams 52, 53, 54 cancontinue to reproduce unread tracks T6, T7, T8, and the reproducing ratebecomes ¾ of the normal rate.

Second, a case that an error occurs on T3 is described. Because lasttailing reproducing beam 51 has arrived at the top of T3 when readout ofthe data for one rotation is finished, any track-jump is not required.Reproducing beam 51 waits until the error-occurrence-address reaches thebeam position with rotation, and tries to reread theerror-occurrence-address. When the rereading can be performed, the datais written into a corresponding address in the buffer memory, and isallowed to be transferred to the host. Heading reproducing beam 54 cancontinue to reproduce T6, and the reproducing rate becomes ¼ of thenormal rate.

Third, when an error occurs near the top of T4 and theerror-occurrence-address can be passed after the track-jump, it is alsopreferable that the track-jump is not performed and rotation waiting isperformed until last tailing reproducing beam 51, light receivingelement 41, and reproducing circuit 71 arrive near the top of T4. Thus,because data can be read out without any track-jump, reduction of thereading rate can be restrained. At this time, the reproducing rate is ¼of the normal rate, because heading reproducing beam 54 can continue toreproduce T6.

FIG. 5 shows the reproducing operation in the present invention using aflowchart. At the beginning of the reproduction operation, four data aresimultaneously read in parallel from four tracks, and existence of anyerror is checked. For the track having no error the data is written intothe buffer memory, and for the track having an error the error addressis written into memory 20. After the tracks rotate once, the data havingno error is transferred to the host. After that, when reproducing of theerror-occurrence-address is confirmed and any error is not found, thereproducing is continued by jumping to a next new unread track. When anerror occurs, it is checked whether the track-jump is carried out forreproducing the error. At this time, execution of the track-jump isselected and an optimal position of the track-jump is set so as torestrain the reduction of the reading rate to a minimum, depending onwhether the track are concentric or spiral and which position on thecircumference on which track the error occurs at. More specificdescription is carried out in the following embodiment.

Even when number of simultaneous readable tracks is larger or smaller,heading light receiving elements (positioned on the outer radius side ofthe track assigned for reading the error-occurrence-track) andreproducing circuits (corresponding to the light receiving elements) cansimilarly continue to reproduce the unread regions. When reading errorsoccur at a plurality of addresses, heading light receiving elements andreproducing circuits can similarly continue to reproduce the unreadregions by performing the following process: the track-jump is performedon the basis of the earliest heading error-occurrence-address on thelast tailing track (positioned on the innermost radius side) oferror-occurrence-tracks, i.e. an error-occurrence-address at which lightreceiving elements earliest arrive from the tops of the tracks withrotation of the disk.

An estimating method for the reproducing rate depending on whether thetrack-jump is performed or not is not restricted to the embodimentdiscussed above. For each system, an estimating method where performancecan be estimated to further improve can be selected.

Rereading is tried, after the data on the already read tracks is jumpedbecause of no requirement of the rereading and last tailing lightreceiving element 41 is jumped onto the error-occurrence-track or atrack after the error-occurrence-track. Thus, the heading lightreceiving element (positioned on the outer radius side of a trackassigned for reading the error-occurrence-track) can continue to readthe unread region. As a result, the reduction of the reading rate duringthe rereading can be minimized.

After the error occurrence, the data reading is continued without anytrack-jump until the data reading on a track being reproduced isfinished, and reading of data on the tracks following theerror-occurrence-track can be completed. Therefore, reading means can beassigned to the unread region corresponding to the already read track.

Preferred embodiment 2

The embodiment 2 of the present invention is described hereinafter withreference to FIG. 2 and FIG. 4. Its basic reading operation is similarto that in the embodiment 1. When a reading error occurs, an address ofthe error position on the disk is stored inreading-error-occurrence-address memory 20.

When tracks are spirally formed, respective reading means reach the topsof next tracks after the disk rotates once for trying the rereading, asshown in FIG. 4.

If the error-occurrence-address is not on a track corresponding to lightreceiving element 41, reproducing beam 51, and reproducing circuit 71,the reading is continued without any track-jump. At this time, a tailingreading means (positioned on the inner radius side of the reading meansassigned to the error-occurrence-track) after a reading means assignedfor the track having an error can reread the error-occurrence-address,and simultaneously the earliest heading reading means (positioned on theoutermost radius side) can read the unread tracks. If the track-jump isperformed, data in a part passed even during the track-jump cannot beread because the disk continuously rotates during the track-jump. Inthis method, however, the track-jump is not performed. Therefore, timeloss for the track-jump is eliminated, and the earliest heading trackcan continue to read the data in the unread regions. As a result, thereduction of the reading rate during the rereading can be minimized.

Preferred embodiment 3

The embodiment 3 of the present invention is described hereinafter withreference to FIG. 2, FIG. 3, and FIG. 4. Its basic reading operation issimilar to that in the embodiment 1. When a reading error occurs, anaddress of the error position on the disk is stored inreading-error-occurrence-address memory 20.

First, the case that tracks are spirally formed is considered. Asdescribed in the embodiment 1, since many reading means are assigned tounread tracks, the reading rate may be reduced when a track-jump isperformed for trying rereading. For example, two following cases areconsidered. When the error-occurrence-address is at the top of a track,the error-occurrence-address is passed during the track-jump and theaddress cannot be reread until one more rotation is finished. When theerror-occurrence-address is on track Tn+1 corresponding to last tailinglight receiving element 41, reproducing beam 51, and reproducing circuit71, the last tailing reading means (positioned on the innermost radiusside) has arrived at the top of the error-occurrence-track after thedata for one rotation is read, and therefore no track-jump is required.As a result, the reading rates, for the cases that the track-jump isperformed and that the track-jump is not performed, are estimated basedon the error-occurrence-address and number of simultaneous readabletracks, and the case that the rate reduction during the rereading issmaller is selected.

Second, in the case that tracks are concentrically formed, thereproducing operation is slightly different. FIG. 3 is a track alignmentdiagram of an information disk on which tracks are concentricallyformed, and reproducing beams 51, 52, 53, 54 respectively trace tracksTn, Tn+1, Tn+2, Tn+3. Reproducing beams 51, 52, 53, 54 move left withrespect to the disk with the rotation of the disk, and return to theiroriginal positions after one rotation. When the error-occurrence-addressis on the track corresponding to last tailing light receiving element41, reproducing beam 51, and reproducing circuit 71, no track-jump isperformed, and the rereading of the error-occurrence-address is triedusing a reading means assigned to the error-occurrence-track. In theother case except that the error-occurrence-address is near the top ofthe track and is passed during the track-jump, the track-jump isperformed and larger number of reading means are assigned to the unreadtracks.

As discussed above, since any unnecessary track-jump is not performedfor rereading in the error occurrence, time for the track-jump is notrequired. When the track-jump is performed, the heading track cancontinue to read data in the unread region even during rereading in theerror occurrence. Therefore, the reduction of the reading rate duringthe rereading can be minimized.

Preferred embodiment 4

The embodiment 4 of the present invention is described hereinafter. Itsbasic reading operation is the same as that in the embodiments 1, 2, 3.In a case that number of error-occurrence-addresses is two or more, areference error-occurrence-address used when the last tailing readingmeans is jumped to the error-occurrence-track or a tailing track(positioned on the inner radius side of the error-occurrence-addresses)after the error-occurrence-addresses on the disk and a referenceerror-occurrence-address used for evaluating whether a track-jump isperformed or not are defined as follows. The referenceerror-occurrence-addresses are defined as thereading-error-occurrence-address closest to the top of the last tailingtrack (positioned on the innermost radius side) of the tracks havingerrors, i.e. the error-occurrence-address which light receiving elementsearliest reach from the tops of the tracks due to rotation of the disk.Thus, even when reading errors occur at a plurality of addresses, therereading of all error-occurrence-addresses can be tried using anyreading means during one rotation of the disk after the track-jump.

As discussed above, even when number of error-occurrence-addresses istwo or more, since any unnecessary track-jump is not performed forrereading in the error occurrence, time for the track-jump is notrequired. In addition, the heading reading means (positioned on theouter radius side of the reading means assigned to theerror-occurrence-tracks) can continue to read data in the unread regioneven during rereading in the error occurrence. Therefore, the reductionof the reading rate during the rereading can be minimized.

Preferred embodiment 5

The embodiment 5 of the present invention is described hereinafter. Anoperation when rereading of the error-occurrence-address is finished isdescribed. The operation when the rereading of theerror-occurrence-address is finished is considered to be the samebetween disks on which data is formed concentrically and spirally,respectively.

For example, when a reading-error occurs at a position ½ rotation awayfrom the top of T2, reproducing beams 51, 52, 53, 54, light receivingelements 41, 42, 43, 44, and reproducing circuits 71, 72, 73, 74 arerespectively assigned to T2, T3, T4, T5, and T5 is assigned to be anunread track. In this case, a reading rate of the unread track duringthe rereading operation is about ¼ of the normal rate, because data ononly one track of four simultaneously readable tracks can be read out.It is assumed that the error-occurrence-address at the position ½rotation away from the top of T2 is successfully reread, the track-jumpis performed, and reproducing beams 51, 52, 53, 54 are respectivelyassigned to T4, T5, T6, T7. Because T4 has been already read, thereproducing rate during ½ rotation is ¾ of the normal rate. Because thereproducing head is positioned at the top of T5 after the ½ rotation,the reproducing rate becomes {fraction (1/1)}.

After the track-jump, however, the read data during the rereading mustbe considered invalid, because data passed during the track-jump cannotbe read out until the disk rotates once. An average rate from thebeginning of the rereading to the finishing of one rotation, for thecases that the track-jump is performed and that reading is continuedwithout any track-jump, are estimated, and the case that rate reductionis smaller must be selected. In this example, the average reading ratefrom the beginning of the rereading to the finishing of one rotation is(¾)*(½)=⅜ of the normal rate. This value is higher than the reading rate¼ derived when no track-jump is performed after rereading, andtherefore, performing of the track-jump just after the finishing of therereading can further decrease the reduction of the reading rate.

Next, when a reading-error occurs at a position ¾ rotation away from thetop of T2, reproducing beams 51, 52, 53, 54, light receiving elements41, 42, 43, 44, and reproducing circuits 71, 72, 73, 74 are respectivelyassigned to T2, T3, T4, T5, and T5 is an unread track, the followingresult is derived. In this case, the reading rate of the unread trackduring the rereading operation is about ¼ of the normal rate, becausedata on only one track of four simultaneously readable tracks can beread out. It is assumed that the error-occurrence-address at theposition ¾ rotation away from the top of T2 is successfully reread, atrack-jump is performed, and reproducing beams 51, 52, 53, 54 arerespectively assigned to T4, T5, T6, T7. Because T4 has been alreadyread, the reproducing rate during ¼ rotation is ¾ of the normal rate.After the ¼ rotation, the reproducing rate is {fraction (1/1)} becauseit is positioned at the top of T5. When the track-jump is performedduring the rereading, the read data is considered invalid because datapassed during the track-jump cannot be read out until the disk rotatesonce. An average rate from the beginning of the rereading to thefinishing of one rotation is (¾)*(¼)={fraction (3/16)} of the normalrate. This value is lower than the reading rate ¼ derived when of notrack-jump is performed after rereading, and therefore, performing notrack-jump just after the finishing of the rereading can furtherdecrease the reduction of the reading rate.

When reading rates between the case that the track-jump is performed andthe case that no track-jump is performed are equal to each other afterthe finishing of the rereading, the data cannot be read during thetrack-jump, and therefore, the method in which no track-jump isperformed further increases the reading rate.

An operation after the finishing of the rereading of theerror-occurrence-address is hereinafter summarized.

When the track-jump is performed just after the finishing of therereading of the error-occurrence-address, the same number of readingmeans as the case that no reading error occurs can be assigned to theunread tracks, and larger number of reading means than that during therereading can be assigned to the unread tracks. When number oferror-occurrence-addresses is two or more, a similar effect isobtainable by performing the track-jump after the finishing of therereading of all error-occurrence-addresses. However, if the track-jumpis performed from the beginning of the rereading before the finishing ofthe reading of the data for one disk rotation, the already read data onthe unread track must be abandoned. That is because the disk continuesto rotate even during the track-jump, a part passed during thetrack-jump on the unread track cannot be read until the finishing of onedisk rotation after the track-jump, and therefore, the data on thealready read part must also be reread. Therefore, on the preconditionthat the data on the unread track which is read during the rereading ofthe error-occurrence-address is abandoned after the track-jump, and onthe basis of number of unread tracks and the error occurrence positionon the track, a method that further decreases the reduction of thereading rate must be selected from the following two methods:

(1) The track-jump is performed just after the finishing of therereading of the error-occurrence-address;

(2) The reading of the track being read is continued until the finishingof the reading of the data for one disk rotation.

In addition, by combining the method with the track-jump during therereading of the error-occurrence-address in the embodiments 1, 2, 3, 4,a more effective operation can be expected.

As discussed above, the method that further decreases the reduction ofthe reading rate is selected from the following two methods:

(1) The track-jump is performed just after the finishing of therereading of the error-occurrence-address, and larger number of readingmeans are assigned to the unread track;

(2) The reading of the data on the track being read is continued.

Therefore, the reduction of the reading rates due to the rereading canbe minimized.

Preferred embodiment 6

The embodiment 6 of the present invention is described hereinafter. Whennumber of error-occurrence-addresses is two or more, estimation of thereading rate becomes complicated. The simplest method is to evaluatewhether the track-jump is performed or not after the finishing of therereading of all error-occurrence-addresses. However, for furtherdecreasing the reduction of the reading rate, the following evaluationis performed.

It is assumed that reading errors occur at a position ½ rotation awayfrom the top of T2 and a position ¾ rotation away from the top of T4,reproducing beams 51, 52, 53, 54, light receiving elements 41, 42, 43,44, and reproducing circuits 71, 72, 73, 74 are respectively assigned toT2, T3, T4, T5, and T5 is an unread track. When thereading-error-occurrence-address at the position ½ rotation away fromthe top of T2 is successfully reread and then a track-jump is performed,the other reading-error-occurrence-address of T4 exists after more ¼rotation, and therefore reproducing beams 51, 52, 53, 54 can berespectively assigned to T4, T5, T6, T7. Because T4 has been alreadyread, the reproducing rate during the subsequent ½ rotation is ¾ of thenormal rate, and the reproducing rate after the ½ rotation becomes{fraction (1/1)} because T4 is positioned at the top of T5. The data onT5 read before the track-jump becomes invalid, and an average readingrate between the beginning of the rereading and the finishing of onerotation becomes (¾)*(½)=⅜ of the normal rate. This value is higher thanthe reading rate ¼ derived when no track-jump is performed afterrereading, and therefore, performing of the track-jump just after thefinishing of the rereading can further decrease the reduction of thereading rate. After that, when rereading of the error-occurrence-addresson T4 is finished, the reading rate for one rotation is recalculatedsimilarly to the case of T2 based on the error-occurrence-address on T2,and whether track-jump is performed after rereading of T4 is determined.

The basic operation is the same as the method for performing thetrack-jump after the rereading of the reading-error-occurrence-addressas described in the embodiment 5. When reading errors occur on aplurality of tracks, depending on the positional relation among theerror-occurrence-addresses, the following method may be expected toincrease the reading rate:

(1) The track-jump is performed after the finishing of the rereading ofall error-occurrence-addresses on the last tailingerror-occurrence-track; and

(2) Larger number of reading means are assigned to the unread track.

For example, it is the case that reading errors occur near the top of atrack assigned to the last tailing reading means (positioned on theinnermost radius side) and at the rear part on a track assigned to theearliest heading reading means (positioned on the outermost radiusside). In this case, the reading means cannot be assigned to the unreadtracks during the rereading of the error-occurrence-addresses.

When the track-jump is performed just after the finishing of therereading of the error-occurrence-address (positioned on the innermostradius side) on the last tailing track so as to assign the last tailingreading means (positioned on the innermost radius side) to a remainingreading-error-occurrence-address, (number of simultaneously readabletracks—1) of tracks can be assigned to the unread tracks. Even in othercases, reading rates in the cases that the track-jump is performed andthat no track-jump is performed are estimated based on the number of theunread tracks and the error-occurrence-addresses on the tracks, and oneof the following processes is selected every finishing of allreading-error-occurrence-addresses on the track assigned to the lasttailing reading means (positioned on the innermost radius side):

(1) The track-jump is performed;

(2) The reading of the track being read is continued.

In addition, by combining the process with the track-jump during therereading of the error-occurrence-address in the embodiments 1, 2, 3, 4,more effective operation can be expected.

Even when number of simultaneously readable tracks is larger or smallerin all embodiments discussed above, a similar process can be carriedout.

In these embodiments, descriptions about an optical disk are given. Fora magnetic disk, a magnetic head can used instead of optical pickup 5.

The estimating methods of the reproducing rate depending on whether thetrack-jump is performed or not are not restricted to the embodimentsdiscussed above. In each systems, an estimating method can be selectedin which improvement of the reproducing rate can be expected.

In the embodiments discussed above, examples using the optical disk aredescried. A similar effect is expectable for an information disk systemsuch as the magnetic disk or a magneto-optical disk.

While the cases that data is recorded from the inner radius to the outerradius on the disk are illustrated in the embodiments 1 to 6, thesimilar method can be carried out even for a disk on which data isrecorded from the outer radius to the inner radius. Positional relationamong the heading track, the tailing track, the reproducing beams, thelight receiving elements, and the reproducing circuits in this case isreverse to the disk on which the data is recorded from the inner radiusto the outer radius.

INDUSTRIAL APPLICABILITY

In a reading-error recovery method in the present invention, a headingreading means can read data on unread tracks even during rereading of anerror-occurrence-address, and therefore, reduction of the reading rateduring the rereading of the reading-error-occurrence-address can beminimized.

In the reading-error recovery method, an optimal track-jump can beperformed during the rereading of the reading-error-occurrence-addresson a disk on which tracks are concentrically formed. Thus, when thetrack-jump is performed, the heading reading means can continue to readthe data on the unread tracks even during the rereading of theerror-occurrence-address. When no track-jump is performed, a period whenthe data cannot be read due to the track-jump is eliminated, andtherefore the reduction of the reading rate during the rereading of thereading-error-occurrence-address can be minimized.

In the reading-error recovery method, an optimal track-jump can beperformed during the rereading of the reading-error-occurrence-addresseven when reading errors occur at two or more positions. As a result,the reduction of the reading rate during the rereading of thereading-error-occurrence-address can be minimized.

In the reading-error recovery method, larger number of reading means areassigned to the unread tracks after the finishing of the rereading ofthe error-occurrence-address. As a result, the reduction of the readingrate just after the finishing of the rereading of thereading-error-occurrence-address can be minimized.

In the reading-error recovery method, an optimal track-jump can beperformed after the finishing of the rereading of thereading-error-occurrence-address. When the track-jump causes reductionof the reading rate, no track-jump is performed after the finishing ofthe rereading. When the track-jump is expected to improve the readingrate, the track-jump is performed, and larger number of reading meansare assigned to the unread tracks. Therefore, the reduction of thereading rates due to the rereading of thereading-error-occurrence-address can be minimized.

In the reading-error recovery method, an optimal track-jump can beperformed after the finishing of the rereading of thereading-error-occurrence-address, even when reading-errors occur on aplurality of tracks. Therefore, the reduction of the reading rates dueto the rereading of the reading-error-occurrence-address can beminimized.

In the embodiments in the present invention, examples using the opticaldisk are descried. However, the similar effect is expectable for aninformation disk system such as a magnetic disk or a magneto-opticaldisk.

What is claimed is:
 1. A method of performing error recovery whilereading tracks on a disk, said method comprising the steps of: storinginformation related to a location where an error has occurred whilereading from said disk; calculating an effective reading rate if saidlocation is reread without a track jump; calculating a further effectivereading rate if said track jump is performed prior to rereading saidlocation, wherein an amount of said track jump is based on: a) in whichone of said tracks said error has occurred; and b) wherein said one ofsaid tracks, said error occurred, comparing said effective reading ratewith said further effective reading rate; and determining whether tomake said track jump prior to rereading said location based on a resultof said comparison.
 2. A method of performing error recovery accordingto claim 1, wherein said tracks are spiral.
 3. A method of performingerror recovery according to claim 1, wherein said tracks are concentric.4. A method of performing error recovery according to claim 1, furthercomprising the step of performing a further track jump in the middle ofrereading said one of said tracks.
 5. A method of performing errorrecovery according to claim 1 further comprising the step of performinga further track jump at the end of rereading said one of said tracks. 6.A method of performing error recovery according to claim 1, wherein saidtrack jump is for a number of tracks corresponding to a number of lightreceiving elements reading said disk if no error has occurred.